REG[6.3->6.4]MDI application blinks when OpenGLWidget is added.

In an MDI application with an MDI area. When an MDI subwindow that contains OpenGL (QOpenGLWidget or QWebEngineView) is added, the application window briefly gets hidden and shown again, i.e., it "blinks".

Attached example reproduces it.
In the document Note does talks something similar
https://doc.qt.io/qt-6/qopenglwidget.html#resource-initialization-and-cleanup

If this is something not going to be fixed, then can there be any workaround?